Camera has become the necessary equipment in people's life today, which adds a good many happy moment in life and records colorful life. With the popularization of camera, the assistant devices to provide carious additional functions for it also become more and more. View finder is the most part of camera, but most of what people commonly maintain and take care while in use is lens, and few people provide view finder with protection. Therefore, after using for a period of time, the view finder will be covered with dust, or more seriously, some of them may often suffer scuffing. The abovementioned phenomenons are common in former 120 cameras. For most of waist level finders, if there is not corresponding protective device, the view finder will be absolutely suffered with dust deposition and damage, and the accumulated dust is not easy to clean up, even more, the image on the view finder screen will not be seen clearly due to the interference of strong light and the view effect will be seriously affected. For the LCD view finder of digital camera in gradual popularization in recent years, because it is exposed outside directly, the abovementioned phenomenons of dust deposition and scuffing are more serious comparing with old-style 120 camera. At the same time, due to the specificity of LCD view finder, the observing effect is not good during side view, which is more serious under the condition of stronger sunlight.